A buyer-seller watermarking protocol

Digital watermarks have previously been proposed for the purpose of copy protection and copy deterrence for multimedia content. Copy deterrence using digital watermarks is achieved by inserting a unique watermark into each copy of the watermark content sold which could be used to trace unauthorized copies to the erring buyer. One problem with such an approach is the fact that the buyer whose watermark has been found on unauthorized copies can claim that the unauthorized copy was created or caused (for example, by a security breach) by the seller. In this paper we propose an interactive buyer-seller protocol for invisible watermarking in which the seller does not get to know the exact watermarked copy that the buyer receives. Hence the seller cannot create copies of the original content containing the buyers watermark. However, in case the seller finds an unauthorized copy, he/she can identify the buyer from whom this unauthorized copy has originated and furthermore can also prove this fact to a third party by means of a dispute resolution protocol. Hence, the buyer cannot claim that an unauthorized copy may have originated from the seller.